A federal judge authorized a summons Wednesday requiring the largest Bitcoin service in the U.S. to provide the IRS records of every user who traded on the site between 2014 and 2015. Covering the identities and transactions of millions of customers, the request to Coinbase is believed to be the largest single attempt to identify tax evaders using virtual currency. The "John Doe" summons targets a particular group or class of taxpayers -- rather than individuals -- the agency has a "reasonable basis" to believe may have broken the law. According to the New York Times, the IRS argued that two cases of tax evasion involving Coinbase combined with Bitcoin's "relatively high level of anonymity" serve as that basis.